Issue 35

X.C. Arnoult et alii, Frattura ed Integrità Strutturale, 35 (2016) 509-522; DOI: 10.3221/IGF-ESIS.35.57 514 It was observed that at higher tempering temperatures delamination cracks increase both in number and in length, then decrease both in number and in length when the tempering temperature reaches 700°C. Yang et al [2] observed for API X70 pipeline steel a temperature dependence on the appearance of the fracture surface. At -60°C, specimen 10 mm thick and in T-L orientation showed a ductile fracture whereas at -20°C, authors observed some delamination cracks on the fracture surface. Joo et al [9] showed also an orientation dependence on the Charpy impact toughness. This could probably be explained by the development of delamination cracks during the fracture process. The API X80 [9] T-L and L-T oriented specimen had a ductile failure between 25°C and -60°C, with the presence of delamination cracks on fracture surface for temperatures from -20°C to -60°C, and cleavage failure mode without delamination cracks at -80°C and - 100°C. Figure 6 : Charpy specimens’ orientation [9]. Figure 7 : Charpy impact test as function of temperature a) , as function of orientation b) , fracture surface of L-T orientation of Charpy specimens broken at room temperature c), -60°C d), and -100°C e) [9]